TEMPERATURE Flashcards
Why is temperature important?
It influences aircraft performance (how efficient the engines are, altitude we can fly at etc). Indicates likelihood of icing etc.
How does temperature affect the atmosphere?
Unequal heating within the atmosphere drives the “weather machine” by setting up pressure gradients that give us wind and frontal systems.
How to convert F to C
C = (F-32) x5/9
Define Solar radiation
Short wavelength, high energy radiation from the sun that heats the earth/atmosphere.
Define terrestrial radiation
Long wavelength, low energy radiation emitted by the earth back into the atmosphere and space.
Describe the balance of solar and terrestrial radiation
For earths temperature to remain at 15deg, incoming solar radiation must balance outgoing terrestrial radiation.
How has global warming affected the balance between solar and terrestrial radiation?
Increase of CO2 in the atmosphere increases absorption of outgoing terrestrial radiation, causing atmosphere to warm up.
Describe how solar & terrestrial radiation affects daily temperature;
-lowest temp?
- balance during the day?
- highest temp?
- Long wave terrestrial radiation occurs all night, meaning the lowest temperature is reached just after dawn (nil incoming short wave radiation at this point).
- Solar radiation increases with the sun’s elevation.
- As the ground warms however, the rate of loss by long wave radiation also increases.
- After midday, short wave intensity starts to decrease, long wave is increasing, two rates become equal 3 hours after midday, this is the time of Max temp.
How does latitude affect air temperature?
Equator vs poles?
At the equator, midday rays from the sun strike the earth almost perpendicular = maximum heating & high daily temps.
At the poles, the sun angle (even in summer), is very low, heating is therefore low & results in cold temps.
How does air temperature affect the seasons?
Equator vs poles?
Equator: regardless of the time of year, the sun beats down & therefore temp changes across the seasons aren’t so stark = “wet” & “dry” season.
Poles: Sun in below the horizon for the winter months, temp falls rapidly as terrestrial radiation continues regardless with no solar radiation to offset.
Therefore, the temp gradient between the south poe & equator are much greater in the winter.
How do strong winds affect air temperature?
The diurnal variation (daily fluctuation) of air temp tends to be greater when winds are calm. Strong winds promote mixing, the gain of heat by day and loss by night occurs through a greater depth in the atmosphere and therefore there is less range in temp.
How does wind direction affect air temp
Southerly = cold, northerly = warm (SH)
How does cloud cover affect air temperature?
Daily fluctuation of temp range is reduced as the cloud layer will reflect incoming solar radiation during the day, reducing daytime temps. At night, it will absorb the outgoing terrestrial radiation & re-radiate this back down to earths surface keeping night time temps warmer.
How does coastal vs. inland location affect daily temperature?
Sea surface temps are slow to change. Temps near the coast will therefore be cooler by day, and warmer by night.
Inland temps can be more extreme (high during the day, lower at night) without the tempering effect of the sea.
How does surface type affect air temperature?
Different surfaces will heat up at different rates - mostly due to their colour. darker surfaces will generally heat up quicker.
How does heat transfer occur in the atmosphere?
Radiation
Conduction
Convection
Advection
Define conduction with relevance to heat transfer in the atmosphere
Heat transfer by touch.
Air is a poor conductor, so it only occurs within a shallow layer about 10cm from the surface.
Define convection with relevance to heat transfer in the atmosphere
Heat transfer by vertical movement of air mass.
Process relies on the atmosphere changing density as temperature changes. Is an important method of heat energy transfer in the atmosphere (particularly from equator to poles)
What does convection do with water vapour
Transports large quantities of water vapour aloft which releases latent heat into the atmosphere when condensation occurs.
Define advection with relevance to heat transfer in the atmosphere
Horizontal heat transfer by wind. (e,g, warm humid air from the tropics)
How is incoming solar energy distributed? (%)
51% absorbed by land & sea
20% reflected by clouds
16% Asorbed by the atmosphere
6% reflected by atmosphere
4% reflected from earths surface
3% absorbed by clouds
How is outgoing terrestrial radiation distributed? (%)
64% radiated to space
23% transferred to atmosphere by latent heat release
15% LW radiation absorbed by atmosphere
7% Conduction & rising air
6% radiated directly to space from earth
What does the rise in temp of the earth’s surface depend on?
The angle of the sun’s rays, surface type, depth of heat penetration & specific heat of the material
Define Albedo
Snow vs forest vs sea?
A measurement of the amount of incident radiation that is REFLECTED.
E.g.snow reflects most radiation & therefore has a HIGH albedo. Forests on the other hand absorb a lot of radiation & therefore have a LOW albedo.
The sea will absorb a lot of radiation if the sun is high, but reflect most of it if the sun is low?
Define specific heat
The SH of a substance is the quanitity of heat energy required to raise the temperature of unit mass of the substance by 1deg. The SH of a substance indicates it’s resistance to change temp.
E.g. water has a high SH, land surfaces have a low SH (low resistance)
Define seasons with reference to temperature/heat
Tilt of earths axis & annual orbit around the sun both affect the amount of solar radiation received at the earths surface.
Seasons are based on average temperature (not position of earth relative to the sun)..
Variation of temperature with height?
Why is this important?
Atmosphere is heated from below, therefore temp generally decreases with height. except in the case of inversions (increase of temp) & isothermal layers (no change).
This lapse rate is critical to determine likelihood of TS, Turb, stability etc.
Process for radiation inversion?
Common alt?
- Overnight, SKC conditions
- Earth loses LW radiation overnight & cools down
- Air in contact with the ground also cools (conduction & low level mixing).
- can reach up to 100-300ft.
The air that is higher than this is not subject to mixing/cooling & will therefore be warmer compared to colder temps at SFC = inversion
Process for turbulence inversion?
Common alt?
Cloud associated?
Created at the top of a friction layer. (between 1000-5000ft, common between 2000-3000ft)
- Wind of >10kts blowing over SFC obstacles.
(depth of turb/friction layer is a result of wind strength & size of obstacles) - turbulent air = lifting = less pressure & therefore cools & expands adiabatically. vice versa for falling air.
- Cooling in top half of layer is offset by warmer air in bottom half = steeper ALR of 3deg/1000ft.
- Air about friction layer is unaffected & therefore warmer than the layer of cold air below = inversion.
Sc cloud can sometimes sit capped by the inversion if there is sufficient moisture.
Process for subsidence inversion?
Common alt?
Cloud associated?
Begin in the upper troposphere during initial formation of developing SFC high.
- High level air begins to converge & SINK
- Sinking air is subject to increasing pressure & compressed & warms adiabatically.
- Subsidence inversion is first created in mid troposphere, descending & becoming stronger by about 8000-3000ft.
- Underneath this, normal ELR is unaffected, so therefore the air is cooler beneath.
Due to subsidence inversion starting in the upper troposphere, where the air is very dry, there is likely to be little-no cloud - and a likely decrease in RH
Process for Frontal inversion?
Common alt?
Cloud associated?
occurs at any frontal surface where warm air is forced to rise up & over a cold air mass.
(Warm air is higher than cold =inversion)
How do inversions effect aviation?
- forms clouds
- Reduces vis
- Turbulence
- Dew point
- Wind shear
- Aircraft performance
How does cloud created by inversions impact us?
Turb inversions: StratoCu is usually created by turb inversions OR , generically as a developing cumuliform cloud that, on reaching a strong (or weak) inversion stops growing and flattens out, or punches through (& flattens out slightly)
Radiation inversions: very low cloud or fog due moisture being trapped below the inversion
Weak inversions: layered cloud at higher levels
How do inversions impact visibility?
Inversion = blanket that traps low level pollutants.
Reduced vis, particularly coastal/cities
How do inversions impact turbulence?
Light mechanical turb is common below inversions, with likelihood of wind shear being present between the smooth layer above and the turbulent air below.
How do inversions impact dew point?
Inversions trap most of the vertical movement of moisture from the earth’s SFC. This means that water vapour content will increase, and therefore dew point temp will also increase.
How do inversions impact aircraft performance?
Turbulence & windshear.
Some degradation when passing through an inversion. Due to the air within the inversion being less dense than the air below (due to being warmer, and also increase in alt = decrease in pressure).
Which gases are the primary heat absorbers?
CO2, Ozone, water vapour
